coin COURIER International journal of high energy physics Investir pour Tenergie, Tindustrie, la recherche, la sante, I'environnement et la defense. Cest le role du CEA. 1 7 000 passionnes de science et de technologie se consacrent a cette mission. Pour preparer I'avenir, ils investissent dans toutes les disciplines scientifiques liees a Tatome. Au CEA, I'avenir c'est innovation et le progres des connaissances. L'ATOME, DE LA RECHERCHE A L'INDUSTRIE ISSN 0304-288X Advertising enquiries Europe Volume 37 No. 7 Micheline Falciola September 1997 Covering current developments in high energy Advertising Manager CERN physics and related fields worldwide CH-1211 Geneva 23, Switzerland Editor: Gordon Fraser Tel.: +41 (22) 767 4103 CERN.COURIER® CERN.CH Fax: +41 (22) 782 1906 Production and Advertisements: Micheline Falciola Rest of the world Micheline_Falciola @ cern.ch Guy Griffiths Advisory Board: E.J.N. Wilson (Chairman), E. Lillestol, Advertising Manager, USA M. Neubert, D. 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CERN's LHC proton collider will be equipped with 'beam screens' to shield the surrounding superconducting USA: Controlled Circulation magnets from radiation emitted by the beams. However the slits allow residual Periodicals postage paid at St. Charles, gas molecules to pass through and become 'frozen' to the walls of the ultra Illinois cold beam pipe (Photo CERN AC. 15.5.97). CERN Courier, September 1997 III te point de depart pour I'electronique u l@@kirt§ for ntr for vacuum Haute precision 11 count on? pour votre progres! 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The hermetic TO-8 package of the o detector has a light tight, vacuum tight 1 mil (25 pm) Beryllium u window to permit soft X-Ray detection. The system resolution with N NOISE a test pulser is 200 eV FWHM. T 350 eV Power to the XR-100T is provided by the PX2T Power Supply. The s PX2T is AC powered and also includes a spectroscopy grade Shaping Amplifier. The XR-100T/PX2T system ensures quick, ENERGY (keV) reliable operation in less than one minute from power turn-on. AMPTEK INC. 6 De Angelo Drive, Bedford, MA 01730-2204 U.S.A. Tel: +1 (617) 275-2242 Fax: +1 (617) 275-3470 e-mail: [email protected] http://www.amptek.com New physics or statistical mirage? Data from the H1 and Zeus experiments at the HERA electron-proton collider at DESY, Hamburg, surprised the world earlier this year by reporting an intriguing excess of backscattered Standard Model electrons (positrons), suggestive of new structure deep inside the proton. With more data, the excesses are still there but less marked, and moreover the two experiments do hamburger not exactly agree. The left-hand box shows the kinematical region with the excess now reported by HI, in which Zeus sees only the expected number of events, while the right- hand box shows the kinematical region with the excess now reported by Zeus, in which H1 sees only the expected number of events! t a major international physics - after the official opening, the first A conference in Munich in 1988, talk of the meeting, by Bruce Straub 0.9 review speaker Don Perkins spoke of of Harvard, covered recent HERA 0.8 a 'festival of the Standard Model'. For results from an integrated luminosity 0.7 almost a decade now, major physics (a measure of the number of 0.6 meetings have continued to be collisions collected) which had 0.5 festivals of the conventional picture increased from 14.2 to 23.7 inverse 0.4 of six quarks and leptons grouped picobarns for H1, and from 20.1 to 0.3 pairwise into three families 33.5 for Zeus. 0.2 interacting via electroweak and inter- The earlier results had covered 0.1 : quark forces. neutral current interactions (with the e methdd All physicists agree that the positron emerging unscathed) for 50 75 100 125 150 175 200 225 250 275 300 M {GeV) Standard Model cannot be the full both experiments, with 2 and 12 e M (GeV) picture, with too many free backscattered events, compared to DA parameters that can only be an expected signal of a fraction of an measured by experiment, and with event and five events from Zeus and the observed pattern of particle H1 respectively. Earlier this year only his Standard Model summary talk at masses unexplained. But like a H1 reported similar charged current Hamburg, Guido Altarelli of CERN quality waterproof watch, the interactions, with the incident underlined the mismatch between the Standard Model had no visible crack positron swallowed up. H1 and Zeus effects. While pointing to prise the case apart and get at the At Hamburg both experiments to possible new physics implications, mechanism inside. reported charged current effects, in his view a statistical fluctuation However earlier this year (April, Zeus and H1 together seeing 28 was the best 'theoretical' explanation. page 1), the Zeus and H1 backscattered events in a kinematical In other physics sectors, neutrino experiments at the HERA electron- zone where 18 ± 4 are expected. anomalies persist in non-accelerator proton collider at DESY, Hamburg, Turning to neutral current data, suggesting that neutrino types reported an intriguing handful of interactions, the new data from the are not immutable, and can mix, excess of positrons recoiling two experiments is not totally while some specific decay channels backwards from collisions at 27.5 coherent. The 2 and 12 anomalous of B mesons (containing the fifth - GeV with 820 GeV protons. The events from Zeus and H1 have now 'beauty' or 'b' - quark) are not quite in backscattering was suggestive of been supplemented by zero and six order.